MAX203EEWP Transceiver question

Question

I am trying to connect one of the receiver ports of MAX203EEWP (pin 19) through a 2.2k resistor to V- (pin 10 and 17). I want this level to be below -3V to be recognized as a MARK level by the RS232 transceiver and invert it to logic 0 in the CMOS side (pin 20). What I see happening is that the pin 20 goes low for 10-40us and then gets pulled up to 5V. I was thinking keeping the pin 19 below the -3V will keep it at MARK level forever until I remove the resistor in circuit. 
 
 Any reason the receiver side is getting pulled up after a short duration and not staying low forever?

EE3 · Accepted Answer

Thanks for the info. What's your concern of connecting 2.2K from RIN to V-? 
 
 Thanks.

ZhongminYu · Answer

Yes, if voltage input stays Low, the output should be in High, not at LOW. Note both RX receive and TX driver are inverter buffers. If you plan to have "0" output, the input should be "1". Please try it to make sure.

ZhongminYu · Answer

Hello, 
 -3V to -15V should be "1" from the the transceiver. Both RS-232 RX and TX are inverted ( see pic below, which was copied from MAX13235 DS) .You can confirm it with a function generator RIN or TIN to confirm it. I have a little concern about the connection from V- to RIN via a 2.2k R. 
 Thanks 
 Zhongmin

ZhongminYu · Answer

Since the V+ and V- are designed for internal driver usage, it will affect the IC performance if sourcing or draining current from these two pins. But week current should be ok. You need to monitor the V- output to see if ripple in accepted level. 
 Thanks 
 Zhongmin

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MAX203EEWP Transceiver question

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